The present invention relates to an electrolyte containing a gas additive having a high reduction potential and a lithium secondary battery comprising the same. More particularly, the present invention relates to an electrolyte containing a gas additive having a high reduction potential which does not increase the internal pressure of the battery, since it does not generate gases when reacting with lithium ions present in the electrolyte to produce a solid electrolyte interface film, and a lithium secondary battery comprising the same.
Recently, developments in the newest electronics industry have enabled electronic equipment to become smaller and more light-weight, and this has increased the use of portable electronic equipment. For the electricity source of such portable electronic equipment, a battery having a high energy density is required. Thus, lithium secondary batteries have been actively studied. A lithium-transition metal oxide is used as the positive active material, and lithium, a lithium alloy, carbon or a carbon complex is used as the negative active material. A secondary battery is prepared by coating the active material on an electric precipitator in an appropriate thickness and length, or coating the active material itself in the form of a film and winding or laminating it with an insulator separator to make an electrode group, putting it in a container, and then injecting the electrolyte therein.
At the beginning of discharge, lithium ions in an electrolyte of a lithium secondary battery react with a non-aqueous organic solvent and thus a lithium secondary battery produces a solid electrolyte interface film while generating gases. Such gases may be H2, CO2, CH4, C2H6, C3H8, C3H6, etc. depending on the kind of non-aqueous organic solvent in the battery. These gases that are generated at the beginning of battery discharge increase the internal pressure of the battery by approximately 1.5 to 2.5 kgf/cm2 or more. The increase in internal pressure induces modification of the center of a specific side of the battery such as swelling in a specific direction. This causes a local difference in adhesion characteristics between electrode plates in electrode groups of the battery. Thus the characteristics and stability of the battery decrease.
In order to solve the aforementioned problem, a container ranging from 0.40 to 0.60 mm in thickness is used in a rectangular-shaped battery, but this decreases the energy density and increases the weight of the battery. In addition, in order to improve the stability of a secondary battery comprising an electrolyte, a vent or current breaker which emanates internal electrolyte as the internal pressure increases above a certain degree, is constructed therein. However, this causes a risk of misoperation due to the increase in internal pressure.
It is an object of the present invention to provide an electrolyte for a lithium secondary battery containing a gas additive that has higher reduction potential than the organic solvent, and that does not produce gases when reacting with lithium ions to form a solid electrolyte interface film.
It is another object of the present invention to provide a lithium secondary battery that has excellent battery properties such as cycle life, high rate discharge properties, low temperature discharge properties, excellent stability, etc. and that is not modified in appearance when discharged,
In order to achieve said objects, the present invention applies an electrolyte comprising a non-aqueous organic solvent to which is added a gas additive having a high reduction potential compared to the non-aqueous organic solvent, to a lithium secondary battery.